The present invention relates generally to systems for refilling the storage tanks of cryogenic liquid dispensing stations and, more particularly, to an interlock that prevents spills during off-loading of cryogenic liquid from a delivery vehicle to a cryogenic liquid dispensing station.
Liquid natural gas (LNG) is a cryogenic liquid that is plentiful, environmentally friendly and domestically available energy source and, therefore, is an attractive alternative to oil. As a result, LNG is increasingly being used as a fuel for vehicles. This is especially true for fleet and heavy duty vehicles.
Due to the increased use of LNG, dispensing stations for refueling LNG-powered vehicles are becoming more common. LNG dispensing stations typically include at least an insulated tank containing a supply of LNG and a pump that dispenses the LNG to the vehicle or saturation/conditioning components.
The dispensing station is periodically refilled by a delivery vehicle such as a tank truck. The delivery truck features a tank containing a supply of LNG as well as a liquid feed hose in communication with the liquid side thereof and a vapor return hose in communication with the vapor side thereof. LNG is off-loaded from the delivery truck tank by connecting the feed hose to a pump that is on-site and in communication with the dispensing station tank. The vapor return hose is placed in communication with the line between the pump and the dispensing station tank. Vapor from the head space of the dispensing station tank is returned via the vapor return hose to the vapor side of the delivery truck tank to relieve pressure build-up in the dispensing station tank. LNG is transferred from the delivery truck tank to the dispensing station tank when the pump is activated.
It has become common practice in the industry to use the same pump to dispense and or condition the LNG and to off-load the LNG from the delivery truck. For example, the pump dispenses LNG from the tank for use. The pump also off-loads LNG from a transport truck to refill the tank. In such stations, automatic and pneumatically operated valves typically control the piping status so that the station may be configured in either the dispense mode or the delivery truck off-load mode. If by some error or failure the valves are improperly set, however, an upset condition may occur. For example, the station could be configured to off-load LNG when the delivery truck hoses are not connected to the station. In addition, even if the station valves were functioning properly, a delivery truck driver could drive away from the station with the delivery truck hoses still connected (known as a xe2x80x9cdrive offxe2x80x9d) and the station still configured for off-loading LNG. In both situations, spillage of LNG could occur. Such an occurrence is undesirable from the standpoint that LNG is wasted and a hazardous condition for the delivery truck driver and environment could be created.
Alternatively, a pump separate from the station dispensing pump may be used to off-load LNG from the delivery truck. With such an arrangement, the liquid feed and vapor return hoses of the delivery truck are also connected to the off-loading pump inlet and outlet sides, respectively. The valves in such a station are typically configured manually by the delivery truck driver. If the delivery truck driver incorrectly configures the valves, or if the delivery truck driver drives off without disconnecting the liquid feed and vapor return hoses, spillage of LNG may also occur.
Prior art dispensing stations attempt to solve the above problems by providing a check valve in the station line running between the off-loading pump and the connection for the delivery truck liquid feed hose. As a result, one way flow of LNG from the delivery truck through the pump and to the station tank is ensured. A disadvantage of this approach, however, is that a pressure drop occurs across the check valve so that pump prime is adversely effected. Furthermore, a check valve may not be installed in the station line running between the station tank and the connection for the delivery truck vapor return line. As a result, this line may be a source of LNG spills even if a check valve is installed in the station liquid fill line.
The present invention is directed to an apparatus for interlocking a cryogenic fluid dispensing station with a cryogenic fluid delivery vehicle. The dispensing station includes an off-loading port that is connected to a tank mounted on a fluid delivery vehicle. The off-loading port receives cryogenic fluid from the delivery vehicle. A pressure sensor is coupled to the off-loading port to sense the cryogenic fluid pressure at the port. A dispensing station valve is in fluid communication with the off-loading port. The dispensing station valve operates between an open position and a closed position wherein the dispensing station valve closes when the pressure sensor senses a fluid pressure at the port below a predetermined level.
Another aspect of the invention is directed to a method of interlocking a cryogenic fluid dispensing station. The method of interlocking the cryogenic fluid dispensing station includes connecting a tank mounted on a fluid delivery vehicle to an off-loading port of the dispensing station. Cryogenic fluid is delivered from the fluid delivery vehicle to the dispensing station through the off-loading port. The off-loading port senses the fluid pressure of the cryogenic fluid. When the fluid pressure of the cryogenic fluid is below a predetermined level, a valve in communication with the off-loading port is closed.
The following detailed description of embodiments of the invention, taken in conjunction with the accompanying drawings, wherein like characters identify identical parts, provide a more complete understanding of the nature and scope of the invention.